1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
2. Description of the Related Art
In recent years, a technique in which a thin film transistor (also referred to as a TFT) is formed using an oxide semiconductor and is applied to an electronic device and the like has attracted attention. For example, a technique in which a switching element and the like of an image display device are formed using zinc oxide, an In—Ga—Zn—O-based oxide semiconductor, or the like as an oxide semiconductor layer is disclosed in Reference 1 and Reference 2.
In addition, as a structure of a transistor using an oxide semiconductor layer, various structures are proposed. For example, a bottom-gate bottom-contact structure, in which an oxide semiconductor layer is formed over a source electrode layer and a drain electrode layer which are provided over a gate insulating layer, is disclosed in Reference 2 and Reference 3.